Process for the manufacture of 4-nitro-1-aminonaphthalene-5-sulfonic acid



Patented Nov. 27, 1951 PROCESS FOR THE MANUFACTURE OF 4- NITRO 1AMINONAPHTHALENE-5-SUL- FONIC ACID Fritz Oestcrlein, Basel, Switzerland,asslgnor to Ciba Limited, Basel, Switzerland, a Swiss firm N Drawing.Application January 30, 1950, Se-

rial No. 141,342. 1949 3 Claims.

In German Patent No. 133,951 is described a process for the manufactureof 4-nitro-1-aminonaphthalene-5-sulfonic acid. This compound is obtainedaccording to that process by nitrating laminonaphthalene-5sulfonic acidwith sulfuric acid-nitric acid mixture at a temperature of 0 to C. Theproduct thus obtainable contains disturbing impurities and in the patentit is therefore recommended to purify the acid by conversion into thesodium salt. The yield of pure product is unsatisfactory.

The present invention is based on the observation that4-nitro-1-aminonaphthalene-5sulfonic acid is obtained by nitration ofl-aminonaphthalene-E-sulfonic acid directly in practically pure form andin good yield when the nitration is carried out at a temperature whichlies below 0 C.

In carrying out the present process it is advantageous to proceed insuch a manner that the l-aminonaphthalene-lsulfonic acid serving asstarting material is dissolved in concentrated, for example inanhydrous, sulfuric acid, with cooling advantageously at a temperaturewhich is not higher than +5", the solution obtained is cooled to atemperature below 0 and then socalled mixed acid is allowed to flow inwhile care is taken by cooling and correspondingly slow addition of themixed acid, that the temperature does not rise to 0 C. For securityreasons it is to be recommended to carry out the nitration at aconsiderably lower temperature than 0 C., for example to commence theaddition of the mixed acid at -10 to 8 C. and not to let the temperatureof the reaction mixture rise above 2 C. until the introduction of themixed acid is complete. (If the nitration takes place at a temperaturewhich attains the upper limit of 0 C., the yield already becomes reducedto a marked extent.) By the term mixed acid" is to be understood in thiscase a mixture which consists of concentrated sulfuric and concentratednitric acid. For the nitration according to the present process withadvantage a practically anhydrous mixed acid is employed Which consistsfor example of equal parts by weight of nitric acid of highestconcentration and anhydrous sulfuric acid (monohydrate). Thetheoretically necessary quantity of nitric acid produces very goodresults in this nitration and it is therefore to be recommended toemploy no excess or only a very slight excess of nitric acid.

The working up of the reaction mixture when the nitration is completecan take place according to customary methods known per se, for exampleby pouring the mixture on ice, filtering off the precipitated 4nitro1aminonaphthalene-S-sulfonic acid, freeing it from adheringsulfuric acid by washing with concentrated sodium chloride InSwitzerland March 25,

solution and drying the practically pure product thus obtained.

It is surprising that in the present case where the known nitration at atemperature lying above 0 C. yields an impure product, the nitration atonly slightly lower temperature, that is below 0 0., yields apractically pure product.

The followin example illustrates the invention, the parts andpercentages being by weight:

Example 111 parts of l-aminonaphthalene-5-sulfonic acid are dissolved at0 to 5 C. in 450 parts of 100 per cent sulfuric acid. The solution iscooled to -10 to -8 C. and within about one hour a mixture of 31.5 partsof about 99 per cent nitric acid and 31.5 parts of 100 per cent sulfuricacid added drop by drop, the temperature being maintained by coolingbelow 2 C.; 15 to 30 minutes after completion of the addition of theacid mixture the nitration is finished. Thereupon, or after standing forsome time, the reaction mass is poured on about 2000 parts of ice,whereby the 4 nitro 1 aminonaphthalene 5-sulfonic acid producedprecipitates in the form of small yellow crystals. It is filtered off,freed from mineral acid by washing with concentrated sodium chloridesolution and can be dried, for example in vacuum. A practically pureproduct is obtained in very good yield per cent of the theoretical orsomewhat more) Having thus described the invention, what is claimed is:

1. Process for the manufacture of 4-nitro-1- aminonaphthalene-5sulfonicacid which comprises nitrating 1aminonaphthalene-5sulfonic acid at atemperature below 2 C.

2. Process for the manufacture of 4nitro-1- aminonaphthalene5-sulfonicacid which comprises nitrating 1-aminonaphthalene-5sulfonic acid withmixed acid at a temperature below 2 C.

3. Process for the manufacture of 4-nitro-1- aminona-phthalene5-sulfonicacid which comprises nitr-ating 1aminonaphthalene-5sulfonic acid withmixed acid at a temperature below 2 C. and in a medium which ispractically anhydrous apart from the water produced in the reactionitself.

FRITZ OESTERLEIN.

REFERENCES CITED FOREIGN PATENTS Country Date Germany Sept. 6, 1902Number

1. PROCESS FOR THE MANUFACTURE OF 4-NITRO-1AMINONAPHTHALENE-5-SULFONICACID WHICH COMPRISES NITRATING 1-AMINONAPHTHALENE-5-SULFONIC ACID AT ATEMPERATURE BELOW -2* C.